250 PHYSIOGRAPHY AXD GEOLOGY OF THE COASTAL PLAIN PEOVINCE, 



agriculture, and (b) in the manufacture of Portland cement. These two 

 principal uses of the Virginia shell marls are discussed separately in the 

 order named. 



Use in Agriculture. — As a fertilizer lime has wide application on acid 

 poil? or tho«p deficient in lime. Lime has been used to some extent as 

 a fertilizer for many years, but it is only within recent years that con- 

 siderable scientific attention has been directed to its use. Many of the 

 state agricultural experiment stations have investigated the use of lime 

 as a fertilizer. 



The effect of lime upon soils is three-fold: (1) It produces important 

 chemical changes; (2) it changes the physical properties of soils which 

 are deficient in calcium; and (3) it serves as a plant food as it is an 

 essential constituent of many plants. 



Chemically lime tends to break up many refractory minerals whose 

 elements reunite to form other compounds which are soluble and can 

 serve as plant foods. It replaces potash in certain of the silicates, liberat- 

 ing that element in such form that it may be used directly by the plant. 

 If the soil contains much humus or vegetable matter the lime will promote 

 its decomposition, resulting in liberating nitrogen in the form of ammonia 

 which is a valuable plant food. Heavy and continuous liming may be 

 carried to such an excess that the plant food will be liberated more rapidly 

 than the plants can make- use of it. Because of its alkaline nature, one 

 of the most important functions performed by lime when applied to acid 

 soils is the neutralizing of acidity. 



Physically lime ameliorates the texture of the soil. Clay soils which 

 have a tendency to cake upon drying are rendered more open and porous 

 in texture by liming, while loose sandy soils may be rendered more compact 

 and retentive of moisture by liming. 



Professor H. J. Patterson^ states that "most cultivated soils possess 

 a slightly acid reaction. This is generally due to the decomposition of 

 the remains of plants in the soil forming organic acids. On wet soils 

 this condition is more noticeable than on dry soils. The sour humus and 

 organic acids are not only unfavorable to the growth of nitrifying ferments 

 and the root tubercles of leguminous plants, but also are likely to dissolve 

 iron and other compounds which are poisonous to crops. Water-culture 

 experiments have shown that slightly acid solutions are favorable to the 

 growth of plants, and while most soils possess this character to slight 



^Maryland Agriculture Experiment Station Bulletin 66, p. 97. 



